It is known, e.g. from German published specification No. 2,140,875, to assemble within an open-ended launching tube a series of elements including a projectile and an inertial mass bracketing a propulsive charge between them. The projectile and the inertial mass are provided with respective sabots which are driven apart upon detonation of the charge and are intercepted, at opposite ends of the tube, by constrictions letting the projectile and the inertial mass pass through in opposite directions. The impact of the sabots upon the constricted tube ends is reduced by interposed deformable braking rings. Upon a simultaneous interception of the two sabots, the impact is balanced so that the launcher experiences no recoil. Such simultaneity, however, is difficult to achieve in practice even if the mass of the inertial body exactly equals that of the projectile; thus, different coefficients of friction may result in consecutive rather than concurrent engagement of the end barriers by the two sabots. Other problems encountered with this type of launching system include the direct heating of the tube, especially in a succession of firings, by the combustion gases which can escape only slowly from the interior of the tube.